It is known that the main difficulties in canning tuna are obtaining cans of constant weight, so as to avoid production waste, and presenting the consumer with a good-looking product when the can is opened, since this determines the product value to a great extent. Such difficulties are not easy to overcome due to the intrinsic nature of tuna, which is a food product showing ample variations in compactness, density and shape from batch to batch where not even from loin to loin.
Moreover it is obvious that the manufacturer tries to obtain the maximum quantity of finished product from the raw material, which must therefore be treated so as to avoid as much as possible crumbling and loss of liquids that lead to a decrease in weight of the raw material to be canned. Clearly, all of the above must be achieved through a machine that guarantees an adequate productivity, since machines and methods that are too slow result in excessive costs.
A particularly critical phase is the placing of the tuna on the conveyor belt of the canning machine, which feeds the tuna towards the dosing chambers, because the tuna loins to be loaded on the belt are usually too small or too large and therefore require an intervention by the operator who must manually adapt them to the required size.
A first drawback of this feeding method is the damage to the tuna loin that inevitably results from such a manual intervention since the operator must act quickly and in a rough manner, with inescapable wastes of tuna that reduce the yield of the raw material and an inconstant density of the fed product that affects the precision in determining the weight of the tuna cake in the dosing chamber.
Another drawback of the operator's manual intervention is the fact that the experience of the operator in handling the tuna loins significantly affects the quality of the finished product, since the smaller the damage the tuna undergoes in the loading step the greater its value when canned.
Finally, it should be noted that this feeding method requires the presence of at least two when not even three operators to guarantee a continuous feed to the canning machine and to prevent possible irregularities or voids in the feed, that would easily occur in case of use of a single operator who cannot constantly operate in an optimal way.
In the light of the above, it is therefore clear that this initial phase of the tuna canning process is particularly critical because it requires a lot of labor and is thus expensive, slows down the process and may negatively affect the yield and quality of the product.
The canning machine disclosed in US 2003/0097819 A1 includes a feeder with a single conveyor belt and a knife to cut away from a tuna loin a portion of loin that is subsequently pushed by a piston which compresses it in a pair of forming chambers.
The tuna loin is still loaded manually on said conveyor belt and does not undergo any pre-shaping prior to being compressed in the forming chambers.